Recent progress in techniques for the eradication
of invasive species on inhabited islands. By John
Ogden

Island Invasives Conference. 2010
started off well, and ended even better! In January there was a
conference in Auckland entitled “Island Invasives: Eradication and
Management”. This conference was organised jointly by the Centre for
Biodiversity and Biosecurity of the University of Auckland, and Invasive
Species Specialist Group of the International Union for Conservation of
Nature. About 240 people attended, from 26 countries all over the world.
Fifty papers were presented in concurrent sessions over two days, and
some of these were particularly relevant to the Trust’s vision for a
pest-free Great Barrier. In particular, in the session entitled “Social
and Economic Dimensions of Eradications” there were sixteen
presentations, including one from the GBICT outlining our experiences in
attempting to promote our vision. Also in that session there were two
other papers specifically addressing eradications on inhabited islands:
Lord Howe (Ian Wilkinson) and Tristan da Cunha (Karen Varnham). Neither
of these has yet been successfully completed, but neither have they
tried and failed. In both cases, as on Great Barrier, it is an on-going
process of convincing a minority of the population that the risks can be
mitigated and are far outweighed by the long-term economic and
conservation benefits. In the same session there was also a paper
outlining the successful use of volunteer hunting for the control of
pigs on Oahu, Hawaii. Most of these papers, including the paper
presented by the Trust, have been reviewed and accepted for publication
and will become available in 2011.

Tristan da Cunha - a volcanic peak in
the remotest South Atlantic
- the local community are scoping a rat eradication.

Key Paper. November saw the publication of a key review paper:
“Eradication of Invasive Mammals on Islands Inhabited by Humans and
Domestic Animals”, by Steffen Oppel, three other members of the Royal
Society for the Protection of Birds, and Brent Bevan, of the Department
of Conservation, Stewart Island Field Centre. The paper is a review of
all the relevant literature on the topic – with about 70 papers referred
to. An abstract is given below:

Non-native invasive mammal species have caused major ecological change
and species extinctions on many islands. While eradications from
uninhabited islands have been well documented, there is very little to
go on when considering inhabited islands. This paper addresses the
challenges associated with campaigns to eradicate invasive mammals from
islands inhabited by humans and domestic animals.

On inhabited islands, detailed analyses of the social, cultural, and
economic costs and benefits of eradication are required to increase the
probability of local communities supporting the eradication campaign.
The ecological benefits of eradication (e.g., improvement of endemic
species’ probability of survival) are difficult to trade-off against
social and economic costs due to the lack of a common currency. Local
communities may oppose an eradication campaign because of perceived
health hazards, inconvenience, financial burdens, religious beliefs, or
other cultural reasons. Besides these social challenges, the presence of
humans and domestic animals also complicates eradication and biosecurity
procedures (measures taken to reduce the probability of unwanted mammals
re-colonizing an island). For example, houses, garbage-disposal areas,
and livestock-feeding areas can provide refuges for rats and therefore
can decrease the probability of a successful rat eradication campaign.
Transport of humans and goods to an island increases the probability of
inadvertent reintroduction of invasive mammals, and the establishment of
permanent quarantine measures is required to minimize the probability of
unwanted re-colonization after eradication. The authors recommend a
close collaboration between island communities, managers, and social
scientists from the inception of an eradication campaign to increase the
probability of achieving and maintaining an island permanently free of
invasive mammals.

The paper discusses the ‘Conditions for Successful Eradication
Campaigns’ under four main headings: Social Acceptabilty; Costs and
Benefits of Eradication; Reducing the Probability of Invasion to Near
Zero, and Increasing the Probability of Eliminating all Individuals. The
last two headings seem at first to overlap, but one deals primarily with
biosecurity, while the other deals with getting the last rat or feral
cat, and how we know when we’ve got it!

Finally, the ‘Recommendations’ are highly pertinent. The first point
made is that ecosystem restoration (i.e. pest eradication) on inhabited
islands is essentially a social activity, and concern for the urgency of
an eradication cannot preclude the importance of community control over
the associated decisions and project activities. Regular public review
and consultation is part of the process. A fair and transparent
decision-making process may be more important to a community than
technical details or even specific outcomes. Engaging the community at
all stages of the project, from information gathering, to consultation,
to decision making, to on-the-ground eradication work, and to final
evaluation of the results is important. Such a programme avoids a
‘top-down’ approach and is most likely to generate public ownership of
the eradication project. If members of the community see it as their
project and take pride in it, complicated tasks such as maintaining high
biosecurity standards, are more likely to be carried out and enforced by
the community. Links to other ecological and economic benefits, such as
the potential to use the project in tourism businesses will also be
recognised. “Ultimately, eradication projects yield long-term benefits
for native island species only if the benefits for human inhabitants are
strongly linked to biological gains and are economically and socially
sustainable.”